Scheduling neighbor cell measurements for multiple wireless communication systems

ABSTRACT

Techniques for scheduling measurements for cells in multiple (e.g., GSM and W-CDMA) wireless communication systems are described. GSM neighbor cells are categorized based on a number of states. The states are prioritized in a manner to achieve good performance. The GSM neighbor cells are thus assigned different priorities depending on their states. W-CDMA neighbor cells are prioritized relative to the states for GSM cells. All W-CDMA neighbor cells can be assigned the same state, given the same priority, and considered as “one” W-CDMA cell in the scheduling. A cell in the GSM or W-CDMA system is selected based on the priorities of the neighbor cells, and the selected cell is scheduled for measurement in the next available frame. The highest-ranking GSM or W-CDMA cell for each idle frame is thus granted use of that idle frame for measurement.

This application claims the benefit of provisional U.S. Application Ser.No. 60/493,535, entitled “Scheduling Neighbor Cell Measurements,” filedAug. 7, 2003.

BACKGROUND

I. Field

The present invention relates generally to communication, and morespecifically to techniques for scheduling measurements for neighborcells in multiple wireless communication systems.

II. Background

In a Global System for Mobile Communications (GSM) system, a terminalcommunicates with one base station at any given moment but periodicallymakes measurements for neighbor base stations. The base station that theterminal communicates with is referred to as the “serving” cell, and theneighbor base stations are referred to as “neighbor” cells. Themeasurements are made so that the terminal can determine if there areany cells better than the current serving cell. This may be the case,for example, if the terminal is mobile and moves from cell to cell. If abetter cell is found, as indicated by the measurements, then theterminal would be handed from the current serving cell over to thebetter cell, which would then become the new serving cell.

GSM provides gaps in the transmissions on the downlink and uplink tofacilitate measurement for neighbor cells. These gaps have apredetermined duration and are spaced apart by a predetermined timeinterval. The terminal uses the gaps to make measurements for theneighbor cells and then reports the measurement results back to theserving cell.

A multi-mode terminal is capable of communicating with multiple wirelesscommunication systems, such as a GSM system and a Wideband Code DivisionMultiple Access (W-CDMA) system. If the multi-mode terminal is incommunication with the GSM system, then the terminal would makemeasurements for GSM neighbor cells and may also need to makemeasurements for W-CDMA neighbor cells. The gaps in transmission in theGSM system are originally intended for use to make measurements for GSMcells. Thus, using these gaps for other purposes, such as to makemeasurements for W-CDMA cells, may degrade the performance of themeasurements for GSM cells.

There is therefore a need in the art for techniques to schedulemeasurements for neighbor cells in multiple wireless communicationsystems.

SUMMARY

Techniques for scheduling measurements for cells in multiple wirelesscommunication systems (e.g., GSM and W-CDMA systems) are describedherein. To achieve good performance, GSM and W-CDMA neighbor cells areprioritized to determine which cell to measure in each frame availablefor measurement (e.g., each idle frame in GSM).

The GSM neighbor cells are categorized based on a number of states. Eachstate is associated with information indicating, for example, whether ornot timing information and cell identification have been obtained for acell. The states are prioritized in a manner to achieve goodperformance. The GSM neighbor cells are thus assigned differentpriorities depending on their states. The W-CDMA neighbor cells areprioritized relative to the states for the GSM neighbor cells. SinceW-CDMA cells are stateless, as described below, all of the W-CDMAneighbor cells can be assigned the same state, given the same priority,and considered as “one” W-CDMA cell in the measurement scheduling. Acell in the GSM or W-CDMA system is selected based on the priorities ofthe neighbor cells, and the selected cell is scheduled for measurementin the next idle frame. The highest-ranking GSM or W-CDMA cell for eachidle frame is thus granted use of that idle frame for measurement.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 shows a GSM network and a W-CDMA network;

FIG. 2 shows a framing structure in GSM;

FIG. 3 shows an organization for traffic and control channels in GSM;

FIG. 4 shows a timeline for making measurement for a GSM neighbor cell;

FIG. 5 shows a timeline for making measurement for W-CDMA neighborcells;

FIG. 6 shows a process for scheduling measurements for cells in multiplewireless communication systems;

FIG. 7 shows a scheme for categorizing GSM neighbor cells into fivestates;

FIG. 8 shows a process for scheduling measurements for GSM and W-CDMAneighbor cells based on the states shown in FIG. 7;

FIG. 9 shows a scheme for ranking GSM neighbor cells with an Unknownstate;

FIG. 10 shows a scheme for categorizing GSM neighbor cells into sevenstates;

FIG. 11 shows a process for scheduling measurements for GSM and W-CDMAneighbor cells based on the states shown in FIG. 10; and

FIG. 12 shows a block diagram of a multi-mode terminal.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

FIG. 1 shows a public land mobile network (PLMN) 100 that includes a GSMnetwork 110 and a W-CDMA network 120, which is also referred to as aUniversal Terrestrial Radio Access Network (UTRAN). GSM is a radioaccess technology (RAT) that can provide voice service and low to mediumrate packet data service. GSM networks are widely deployed throughoutthe world. W-CDMA is a new radio access technology that can provideenhanced services and capabilities (e.g., higher data rates, concurrentvoice and data calls, and so on). GSM network 110 and W-CDMA network 120are thus two radio access networks employing different radio accesstechnologies (GSM and W-CDMA) but belonging to the same PLMN.

GSM network 110 and W-CDMA network 120 each include multiple cells,where a “cell” can refer to a base station and/or its coverage area,depending on the context in which the term is used. GSM network 110includes base stations 112 that provide communication for terminalswithin the GSM network. A mobile switching center (MSC) 114 couples tobase stations 112 and provides coordination and control for these basestations. GSM network 110 may support General Packet Radio System(GPRS), which provides packet data service for GSM terminals. W-CDMAnetwork 120 includes base stations 122 that provide communication forterminals within the W-CDMA network. A radio network controller (RNC)124 couples to base stations 122 and provides coordination and controlfor these base stations. MSC 114 communicates with RNC 124 to supportinterworking between the GSM and W-CDMA networks.

A multi-RAT terminal 150 (e.g., a dual-mode cellular phone) has thecapability to communicate with GSM network 110 and W-CDMA network 120,typically with one network at any given moment. This capability allows asubscriber/user to obtain the performance advantages of W-CDMA and thecoverage benefits of GSM with the same terminal. Terminal 150 may befixed or mobile and may also be referred to as a user equipment (UE), amobile station (MS), a mobile equipment (ME), a wireless communicationdevice, or some other terminology.

GSM uses different types of channels to send different types of data. Inparticular, traffic or user-specific data is sent on traffic channels,which are assigned to terminals for the duration of a call. Broadcast,control, and other overhead data is sent on control channels.

FIG. 2 shows a framing structure defined by GSM. The timeline for datatransmission is divided into superframes. Each superframe has a durationof 6.12 seconds and includes 1326 TDMA (Time Division Multiple Access)frames. A superframe can be partitioned into either 51 26-framemultiframes (which are mainly used for traffic channels) or 26 51-framemultiframes (which are mainly used for control channels).

FIG. 3 shows an exemplary channel organization for the traffic andcontrol channels in GSM. The traffic channels use the 26-framemultiframe structure. Each 26-frame multiframe includes 26 TDMA frames,which are labeled as TDMA frames 0 through 25. Each TDMA frame has aduration of 4.615 msec. The traffic channels are sent in TDMA frames 0through 11 and TDMA frames 13 through 24 of each 26-frame multiframe. Acontrol channel (SACCH/T) is sent in TDMA frame 12 and is used to carryinband signaling such as (1) measurement reports sent by terminals onthe uplink and (2) timing advances for the terminals sent by the basestation on the downlink. No data is sent in the idle frame (I), which isused by the terminals to make measurements for neighbor cells. Althoughnot shown in FIG. 3 for simplicity, each TDMA frame is furtherpartitioned into 8 time slots. Each active terminal/user is assigned onetime slot for the duration of a call, and user-specific data for theterminal is sent in the assigned time slot. The terminal may measurereceived signal strength (i.e., received signal power) for the neighborcells in the unassigned time slots.

The control channels use the 51-frame multiframe structure. Each51-frame multiframe includes 51 TDMA frames, which are labeled as TDMAframes 0 through 50. The control channels for GSM include a frequencycorrection channel (FCCH), a synchronization channel (SCH), a broadcastcontrol channel (BCCH), and a common control channel (CCCH). The FCCHcarries a tone that allows a terminal to obtain frequency and coarsetiming information for a transmitting cell. The FCCH is sent in TDMAframes 0, 10, 20, 30 and 40 of each 51-frame multiframe. The SCH carries(1) a reduced TDMA frame number (RFN) that is used by a terminal tosynchronize its timing and frame numbering and (2) a base transceiverstation identity code (BSIC) that identifies the transmitting cell. TheSCH is sent in TDMA frames 1, 11, 21, 31 and 41 of each 51-framemultiframe. The BCCH carries system information and is sent in TDMAframes 2, 3, 4 and 5 of each 51-frame multiframe. The CCCH carriescontrol information and is also used to implement a paging channel(PCH), which carries paging messages for idle terminals.

The channel organization for the traffic and control channels in GSM isdescribed in detail in a document 3GPP TS 05.01, which is publiclyavailable.

A GSM system operates on one or more frequency bands. Each frequencyband covers a specific range of frequencies and is divided into a numberof 200 kHz RF channels. Each RF channel is identified by a specificARFCN (absolute radio frequency channel number). For example, the GSM900 frequency band includes ARFCNs 1 through 124, the GSM 1800 frequencyband includes ARFCNs 512 through 885, and the GSM 1900 frequency bandincludes ARFCNs 512 through 810.

Each GSM cell transmits traffic and overhead data on a set of RFchannels that is assigned to that cell by a network operator. To reduceinter-cell interference, GSM cells located near each other are assigneddifferent sets of RF channels, so that the transmissions from thesecells do not interfere with one another. Each GSM cell transmits theFCCH, SCH, and BCCH on one or more of the RF channels assigned to thatcell. An RF channel used to transmit these control channels is referredto as a BCCH carrier.

Each GSM cell that supports Release 97 or Release 98 version of the GSMstandard broadcasts a BCCH allocation list (which is also referred toherein as a neighbor cell list) that can contain up to 32 GSM neighborcells. Each GSM cell that supports Release 99 or later version of theGSM standard and each 3GPP cell broadcasts a neighbor cell list that cancontain up to 32 GSM cells and up to 64 W-CDMA neighbor cellsdistributed across up to three W-CDMA frequencies. The neighbor celllist contains the ARFCN of the BCCH carrier and the BSIC for each GSMneighbor cell in the list. A terminal obtains the neighbor cell listfrom its GSM serving cell and performs measurements for the GSM andW-CDMA neighbor cells included in this list, as specified by 3GPP.

A terminal that is in communication with a GSM serving cell periodicallymakes measurement for cells in the neighbor cell list to look for bettercells. The neighbor cells may use the same RAT as that of the servingcell (i.e., GSM) or a different RAT (e.g., W-CDMA). Because of thefrequency division multiplex nature of GSM, the neighbor cells transmiton different RF channels than those of the GSM serving cell. Thus, inorder to make measurements for the neighbor cells, whether of the sameor different RAT, the terminal needs to tune its RF receiver away fromthe RF channel for the traffic channels for the GSM serving cell. Whiletuned away, the terminal cannot receive data from or transmit data tothe GSM serving cell. GSM creates idle frames to provide the terminalwith some time to tune away from the GSM serving cell, make measurementsfor the neighbor cells, and tune back to the serving cell, all withoutlosing data from downlink/uplink transmissions.

GSM requires a terminal to periodically report the received signalstrength and cell identifier (BSIC) for each cell in the neighbor celllist while the terminal is operating in a GSM dedicated mode (for acircuit-switched voice or data call) or a GPRS packet transfer mode (fora packet data call). In GSM, the cells are not synchronized and thetiming of each GSM cell is unlikely to be aligned with the timing ofother GSM cells. GSM thus further requires the terminal to maintain thetiming of some of the GSM neighbor cells relative to the GSM servingcell. By maintaining synchronization to these neighbor cells, theterminal can be quickly handed over to one of these cells if and whenthe network issues a handover command.

FIG. 4 illustrates a timeline for making measurement for a GSM neighborcell. Because GSM cells are not synchronized, the 51-frame multiframesused for the control channels of the GSM neighbor cell may start at anarbitrary point in time relative to the 26-frame multiframes used forthe traffic channels of the GSM serving cell. The 26-frame multiframeand the 51-frame multiframe are defined such that the FCCH and SCH forthe GSM neighbor cell appear to slide past the idle frames for the GSMserving cell, as illustrated in FIG. 4. At least two TDMA frames areneeded to complete the measurement for the GSM neighbor cell—one TDMAframe to process the FCCH to obtain a coarse estimate of the timing andfrequency of the GSM neighbor cell and another TDMA frame to decode theSCH to obtain a more accurate timing estimate, the RFN, and the BSIC forthe neighbor cell. Since the FCCH and SCH are transmitted every 10 TDMAframes, 11 idle frames are needed in the worst case scenario to find andprocess the FCCH and SCH when the timing of the GSM neighbor cell is notknown.

Each W-CDMA cell continuously transmits a pilot that is scrambled with apseudo-random number (PN) sequence assigned to that cell. The pilot of aW-CDMA cell can be processed to determine the timing of the W-CDMA cell,which is commonly given by the position of the PN sequence (i.e., the PNposition) for the cell relative to a PN counter maintained by theterminal. The terminal also typically measures the signal-to-noise ratio(SNR) of the pilot in order to ascertain the likelihood of the measuredpilot being an actual W-CDMA signal instead of noise. Since the W-CDMApilot is continuous, the terminal can sample the received signal duringan idle frame, store the data samples in a buffer, and process the datasamples off-line (as opposed to real-time during the idle frame).

FIG. 5 illustrates a timeline for making measurement for W-CDMA neighborcells. In W-CDMA, multiple W-CDMA cells can transmit concurrently on thesame frequency. The terminal can thus process the same data samplescollected for a given W-CDMA frequency to make measurements for allW-CDMA cells transmitting on that frequency. W-CDMA cells are statelessin that no information needs to be maintained to indicate what has beengathered or what still needs to be gathered in order to complete themeasurements for these cells (which is not the case for GSM cells). Inorder to comply with the requirements imposed by 3GPP, the terminalneeds to obtain data samples for each W-CDMA frequency at a particularminimum rate (e.g., every seven idle frames for an exemplary design).The sampling interval is the time duration between consecutive idleframes in which data samples are required for one W-CDMA frequency. Ifthe neighbor cell list contains W-CDMA cells at multiple W-CDMAfrequencies, then the terminal can perform the sampling for thesefrequencies in a staggered and interlaced manner, as shown in FIG. 5. AW-CDMA scheduler that is responsible for processing W-CDMA neighborcells can request an idle frame periodically (e.g., every L-th idleframe) to capture data samples for W-CDMA processing. The GSM networksends a 3G_SEARCH_PRIO flag to indicate the priority the terminal shouldgive to measurements for W-CDMA cells versus GSM cells. The value forthe parameter L is determined by the number of W-CDMA frequencies, thedesign of the terminal, the priority of the W-CDMA neighbor cells versusthe GSM neighbor cells, and so on.

The terminal is typically able to measure only one GSM neighbor cell orone W-CDMA frequency in each idle frame because of its short duration.The terminal thus needs to measure the neighbor cells in an intelligentmanner in order to comply with the requirements imposed by 3GPP. Onesuch requirement is for the terminal to identify a strong cell withinfive seconds after being switched on.

FIG. 6 shows a flow diagram of an overall process 600 for schedulingmeasurements for cells in multiple wireless communication systems (e.g.,GSM and W-CDMA networks). In order to comply with 3GPP requirements andachieve good performance, the GSM and W-CDMA neighbor cells areprioritized to determine which cell to measure in the next idle frame(or the next available frame).

The GSM neighbor cells are categorized based on a number of states(block 612). Each state is associated with information indicating, forexample, whether or not timing information and cell identification havebeen obtained for a cell, as described below. The states are prioritizedin a manner to achieve good performance (block 614). The GSM neighborcells are thus assigned different priorities depending on their states.The W-CDMA neighbor cells are prioritized relative to the states for theGSM neighbor cells (block 616). All of the W-CDMA neighbor cells can, ineffect, belong to the same state and be assigned the same priority sinceW-CDMA cells are stateless, as described above. A W-CDMA request fromthe W-CDMA scheduler may be viewed as “one” W-CDMA neighbor cell byscheduling process 600. This one W-CDMA cell would represent all of theW-CDMA neighbor cells operating at the W-CDMA frequency covered by theW-CDMA request. The GSM cells and the W-CDMA cell can be ranked based ontheir assigned priorities. A cell in the GSM or W-CDMA network isselected based on the priorities of the neighbor cells (block 618). Theselected cell is scheduled for measurement in the next idle frame (block620). The highest-ranking GSM or W-CDMA cell for each idle frame is thusgranted use of the idle frame for measurement.

The GSM neighbor cells are effectively categorized into differentgroups, one group for each state, based on the state information forthese cells. These groups/states are assigned different priorities inthe measurement scheduling. The groups/states may be defined in variousmanners. Two exemplary schemes are described below.

FIG. 7 shows a state diagram of a first scheme 700 for categorizing theGSM neighbor cells into five states. These states are defined asfollows:

-   -   Unknown state 710—includes GSM neighbor cells for which the FCCH        and SCH have not been processed.    -   Strong SCH Unknown state 720—includes GSM neighbor cells for        which the FCCH has been detected and which are among the M        strongest received GSM neighbor cells (i.e., the top M cells).    -   SCH Unknown state 730—includes GSM neighbor cells for which the        FCCH has been detected and which are not among the top M cells.    -   Known Confirmed state 740—includes GSM neighbor cells for which        the FCCH has been detected and the SCH has been decoded within        the last T seconds.    -   Known Unconfirmed state 750—includes GSM neighbor cells for        which the FCCH has been detected and the SCH was decoded more        than T seconds ago.        In an embodiment, M=6 and T=10. Other values may also be used        for M and T.

For scheme 700, the GSM neighbor cells are initialized to Unknown state710. Each GSM neighbor cell can thereafter transition from state tostate (or equivalently, from group to group) depending on measurementresults for that cell and/or other pertinent information. The transitionfor one GSM neighbor cell is as follows. This cell initially starts inUnknown state 710. If the FCCH for the cell is detected, then the celltransitions to Strong SCH Unknown state 720 if the received signalstrength for the cell is among the top M cells and to SCH Unknown state730 otherwise. The cell transitions from state 720 to state 730 if itfalls out of the top M cells, and from state 730 to state 720 if itbecomes one of the top M cells.

From states 720 and 730, the cell transitions back to state 710 if theSCH is not found or cannot be decoded after Y attempts or N seconds. Theparameters Y and N are selected to provide the desired performance. Forexample, the parameter Y can be set to three to give the terminal threeattempts at decoding the SCH. The cell transitions from states 720 and730 to Known Confirmed state 740 if the SCH is decoded. The cell remainsin state 740 if the SCH is decoded within T seconds and transitions toKnown Unconfirmed state 750 otherwise. From state 750, the celltransitions back to state 740 if the SCH is decoded and to state 710 ifthe SCH is not found or cannot be decoded after Z attempts. Theparameter Z may be set, for example, to three to give the terminal threeattempts at decoding the SCH.

In an embodiment, GSM neighbor cells in Strong SCH Unknown state 720 aregiven a priority of 1.0, cells in SCH Unknown state 730 are given apriority of 2.0, cells in Known Unconfirmed state 750 are given apriority of 3.0, and cells in Unknown state 710 are given a priority of4.0, where a lower priority number corresponds to higher priority. GSMneighbor cells in Known Confirmed state 740 do not need to be measuredand are not assigned a priority. In an embodiment, the W-CDMA neighborcells are given a priority of 2.5, which is higher than KnownUnconfirmed state 750 but lower than SCH Unknown state 730.

FIG. 8 shows a flow diagram of a process 800 for scheduling measurementsfor GSM and W-CDMA neighbor cells. Process 800 is based on the statediagram shown in FIG. 7 and may be performed after each idle frame.

Initially, measurement results for the most recent idle frame areobtained (block 812). The measurement results may indicate, for example,whether the FCCH has been detected or the SCH has been decoded for theGSM neighbor cell scheduled in the most recent idle frame. The states ofthe GSM neighbor cells are updated based on the measurement results andother pertinent information (block 814). For example, the GSM neighborcell scheduled in the most recent idle frame may transition to (1)Strong SCH Unknown state 720 or SCH Unknown state 730 if the FCCH hasbeen detected, (2) Known Confirmed state 740 if the SCH has beendecoded, or (3) Unknown state 710 if the SCH cannot be decoded after Yor Z attempts have been made. The states of the GSM neighbor cells mayalso change even though these cells were not selected for measurement inthe most recent idle frame. For example, GSM neighbor cells in KnownConfirmed state 740 may transition to Known Unconfirmed state 750 if Tseconds have elapsed since the last SCH decoding. GSM neighbor cells mayalso transition between state 720 and state 730 based on their receivedsignal strength.

For each state, GSM neighbor cells with that state are ranked (block816). The ranking may be based on received signal strength, the amountof elapsed time since the last measurement, cell timing, and so on. Thereceived signal strength for GSM neighbor cells may be measured duringthe unassigned time slots in the TDMA frames used for the trafficchannels. Various ranking schemes may be used to rank the GSM neighborcells for each state. In one ranking scheme, the cells in a given state(e.g., Strong SCH Unknown state 720, SCH Unknown state 730, or KnownUnconfirmed state 750) are scheduled for measurement in sequentialorder, with the cell last scheduled for measurement being ranked thehighest and the cell most recently scheduled being ranked the lowest. Inanother ranking scheme, for a given state, the cell with the highestreceived signal strength is ranked the highest and the cell with thelowest received signal strength is ranked the lowest. A cell may also beranked higher if its timing is known and its SCH is aligned with thenext idle frame. An exemplary ranking scheme for GSM neighbor cells inUnknown state 710 is described below.

A determination is then made whether there are any GSM neighbor cells inStrong SCH Unknown state 720 with an SCH frame potentially aligned withthe next idle frame (block 820). State 720 has the highest priority forprocess 800. Whether or not a given GSM neighbor cell has an SCH framepotentially aligned to the next idle frame may be determined based onthe coarse timing obtained from the detected FCCH for the cell. If theanswer is ‘yes’ for block 820, then the highest-ranking cell that meetsthe conditions in block 820 is scheduled for SCH decoding in the nextidle frame (block 822).

If the answer is ‘no’ for block 820, then a determination is madewhether there are any GSM neighbor cells in SCH Unknown state 730 withan SCH frame potentially aligned with the next idle frame (block 830).State 730 has the second highest priority for process 800. If the answeris ‘yes’ for block 830, then the highest-ranking cell that meets theconditions in block 830 is scheduled for SCH decoding in the next idleframe (block 832).

If the answer is ‘no’ for block 830, then a determination is madewhether there is a pending W-CDMA request, which has the third highestpriority (block 840). If the answer is ‘yes’, then the W-CDMA scheduleris informed that it can use the next idle frame to capture data samplesfor W-CDMA processing (block 842).

If the answer is ‘no’ for block 840, then a determination is madewhether there are any GSM neighbor cells in Known Unconfirmed state 750with an SCH frame aligned with the next idle frame (block 850). State750 has the fourth highest priority for process 800. If the answer is‘yes’ for block 850, then the highest-ranking cell that meets theconditions in block 850 is scheduled for SCH decoding in the next idleframe (block 852).

If the answer is ‘no’ for block 850, then a determination is madewhether there are any GSM neighbor cells in Unknown state 710, which hasthe lowest priority for process 800 (block 860). If the answer is ‘yes’,then the highest-ranking cell with this state is scheduled for FCCHdetection in the next idle frame (block 862). Process 800 terminatesafter blocks 822, 832, 842, 852 and 862 and after a ‘no’ at block 862.

For process 800, the pending W-CDMA request may be assigned higherpriority (e.g., higher than Strong SCH Unknown state 720) if the3G_SEARCH_PRIO flag is set. The network sets this flag to indicate thatW-CDMA neighbor cells should be given higher priority than GSM neighborcells for measurements.

FIG. 9 shows an exemplary ranking scheme 900 for the GSM neighbor cellsin Unknown state 710. For ranking scheme 900, the three strongest GSMneighbor cells with this state are labeled as A1, A2, and A3, the nextthree strongest cells with this state are labeled as B1, B2, and B3, andthe remaining cells with this state are labeled as C1 through CJ. Forranking scheme 900, one B cell is scheduled for measurement after allthree A cells have been scheduled, and one C cell is scheduled after allthree B cells have been scheduled. As shown in FIG. 9, the three A cells(A1, A2 and A3) are scheduled for measurement sequentially, followed bythe highest-ranking B cell (B1), followed by the three A cells, followedby the next highest-ranking B cell (B2), followed by the three A cells,followed by the lowest-ranking B cell (B3), followed by thehighest-ranking C cell (C1), and so on. The three B cells are thusinterlaced with three sets of A cells, and the J C cells are interlacedwith J sets of A and B cells.

FIG. 10 shows a state diagram of a second scheme 1000 for categorizingthe GSM neighbor cells into seven states. These states are defined asfollows:

-   -   Strong FCCH Unknown state 1010—includes GSM neighbor cells that        are among the top M cells and for which the FCCH has not been        detected and the number of failed FCCH detection attempts is        less than X.    -   FCCH Unknown state 1020—includes GSM neighbor cells that are not        among the top M cells and for which the FCCH has not been        detected and the number of failed FCCH detection attempts is        less than X.    -   Strong SCH Unknown state 1030—includes GSM neighbor cells that        are among the top M cells and for which the FCCH has been        detected and the number of failed SCH decoding attempts is less        than Y.    -   SCH Unknown state 1040—includes GSM neighbor cells that are not        among the top M cells and for which the FCCH has been detected        and the number of failed SCH decoding attempts is less than Y.    -   Known Confirmed state 1050—includes GSM neighbor cells for which        the FCCH has been detected and the SCH has been decoded within        the last T seconds.    -   Known Unconfirmed state 1060—includes GSM neighbor cells for        which the FCCH has been detected and the SCH was decoded more        than T seconds ago.    -   Unknown state 1070—includes GSM neighbor cells with more than X        failed FCCH detection attempts or more than Y failed SCH        decoding attempts.

For scheme 1000, the GSM neighbor cells are initialized to either StrongFCCH Unknown state 1010 or FCCH Unknown state 1020 depending on theirreceived signal strength. Each GSM neighbor cell can thereaftertransition from state to state depending on measurement results and/orother pertinent information. The transition for one GSM neighbor cell isas follows. If the FCCH for this cell is detected, then the celltransitions (1) from Strong FCCH Unknown state 1010 to Strong SCHUnknown state 1030 or (2) from FCCH Unknown state 1020 to SCH Unknownstate 1040. If the FCCH for the cell is not detected after X attempts,then the cell transitions to Unknown state 1070. The parameter X isselected to provide the desired performance. For example, the parameterX may be set to 33 to give the terminal at least three attempts atdetecting the FCCH for the worst case scenario when the timing for thecell is not known. The cell transitions between states 1010 and 1020 andbetween states 1030 and 1040 depending on whether or not it is withinthe top M cells.

From states 1030 and 1040, the cell transitions back to state 1070 ifthe SCH is not found or cannot be decoded after Y attempts. The celltransitions from states 1030 and 1040 to Known Confirmed state 1050 ifthe SCH is decoded. The cell remains in state 1050 if the SCH is decodedwithin T seconds and transitions to Known Unconfirmed state 1060otherwise. From state 1060, the cell transitions (1) back to state 1050if the SCH is decoded or (2) to state 1010 or 1020, depending on thereceived signal strength, if the SCH is not found or cannot be decodedafter Z attempts.

In an embodiment, GSM neighbor cells in Strong SCH Unknown state 1030are given a priority of 1.0, cells in Strong FCCH Unknown state 1010 aregiven a priority of 2.0, cells in Known Unconfirmed state 1060 are givena priority of 3.0, cells in SCH Unknown state 1040 are given a priorityof 4.0, cells in FCCH Unknown state 1020 are given a priority of 5.0,and cells in Unknown state 1070 are given a priority of 6.0, where alower priority number corresponds to higher priority. GSM neighbor cellsin Known Confirmed state 1050 do not need to be measured and are notassigned a priority. In an embodiment, the W-CDMA neighbor cells aregiven a priority of 5.5 for scheme 1000.

FIG. 11 shows a flow diagram of a process 1100 for schedulingmeasurements for GSM and W-CDMA neighbor cells. Process 1100 is based onthe state diagram shown in FIG. 10 and may be performed after each idleframe.

Measurement results for the most recent idle frame are obtained (block1112) and used along with other pertinent information to update thestates of the GSM neighbor cells (block 1114). For each state, the GSMneighbor cells with that state are ranked (block 1116). The ranking maybe based on received signal strength, the amount of elapsed time sincethe last measurement, cell timing, and so on, as described above. For agiven state (e.g., Strong FCCH Unknown state 1010, Strong SCH Unknownstate 1030, and so on), cells with that state may be given higherranking for the first P seconds (e.g., P=5) upon transitioning into thestate. The cells in a given state may be ranked based on their receivedsignal strength. The cells in a given state (e.g., Unknown state 1070)may also be ranked in sequential order, with the cell last scheduled formeasurement being ranked the highest and the cell most recentlyscheduled being ranked the lowest. Various ranking schemes may be usedto rank the cells, and this is within the scope of the invention.

A determination is then made whether there is a pending W-CDMA requestand whether the 3G_SEARCH_PRIO flag is set (block 1120). If the answeris ‘yes’ for block 1120, then the W-CDMA scheduler is informed that itcan use the next idle frame (block 1122).

If the answer is ‘no’ for block 1120, then a determination is madewhether there are any GSM neighbor cells in Strong SCH Unknown state1030 with an SCH frame potentially aligned with the next idle frame(block 1130). If the answer is ‘yes’, then the highest-ranking cell thatmeets the conditions in block 1130 is scheduled for SCH decoding in thenext idle frame (block 1132).

If the answer is ‘no’ for block 1130, then a determination is madewhether there are any GSM neighbor cells in Strong FCCH Unknown state1010 (block 1140). If the answer is ‘yes’, then the highest-ranking cellwith this state is scheduled for FCCH detection in the next idle frame(block 1142).

If the answer is ‘no’ for block 1140, then a determination is madewhether there are any GSM neighbor cells in Known Unconfirmed state 1060with an SCH frame aligned with the next idle frame (block 1150). If theanswer is ‘yes’, then the highest-ranking cell that meets the conditionsin block 1150 is scheduled for SCH decoding in the next idle frame(block 1152).

If the answer is ‘no’ for block 1150, then a determination is madewhether there are any GSM neighbor cells in SCH Unknown state 1040 withan SCH frame potentially aligned with the next idle frame (block 1160).If the answer is ‘yes’, then the highest-ranking cell that meets theconditions in block 1160 is scheduled for SCH decoding in the next idleframe (block 1162).

If the answer is ‘no’ for block 1160, then a determination is madewhether there are any GSM neighbor cells in FCCH Unknown state 1020(block 1170). If the answer is ‘yes’, then the highest-ranking cell withthis state is scheduled for FCCH detection in the next idle frame (block1172).

If the answer is ‘no’ for block 1170, then a determination is madewhether there is a pending W-CDMA request (block 1180). If the answer is‘yes’, then the W-CDMA scheduler is informed that it can use the nextidle frame (block 1182).

If the answer is ‘no’ for block 1180, then a determination is madewhether there are any GSM neighbor cells in Unknown state 1070, whichhas the lowest priority for process 1100 (block 1190). If the answer is‘yes’, then the highest-ranking cell with this state is scheduled forFCCH detection in the next idle frame (block 1192). Process 1100terminates after blocks 1122, 1132, 1142, 1152, 1162, 1172, 1182 and1192 and after a ‘no’ at block 1190.

FIGS. 7 and 10 show two exemplary schemes 700 and 1000, respectively,for defining the states of the GSM neighbor cells. In general, anynumber of states and any type of states may be defined, and this iswithin the scope of the invention. Moreover, the states may be assigneddifferent priorities than those described above. Numerous other schemesfor defining the states of GSM neighbor cells may be implemented, andthis is within the scope of the invention.

FIGS. 8 and 11 show two exemplary processes 800 and 1100, respectively,for scheduling GSM and W-CDMA neighbor cells for measurements. Otherscheduling processes may also be implemented, and this is within thescope of the invention. For simplicity, processes 800 and 1100 show allcells with the same state being assigned the same priority (albeitwithin different ranking among the cells with that state). For example,in process 1100, all of the cells with Strong FCCH Unknown state 1010have higher priority than the cells with Known Unconfirmed state 1060. Acell with a lower priority state may also be assigned higher prioritythan cells with a higher priority state. For example, a cell with KnownUnconfirmed state 1060 may be assigned higher priority than cells withstates 1010 and 1030 if the SCH for this cell is aligned with theupcoming idle frame.

The techniques described herein may be used to schedule measurements forneighbor cells in multiple wireless communication systems. For clarity,these techniques have been specifically described for GSM and W-CDMAsystems. These techniques may also be used for other CDMA and TDMAsystems. The CDMA systems may implement IS-2000, IS-856, IS-95, or someother standards, which are known in the art. The neighbor cells forthese systems may have state (such as for GSM) or may be stateless (suchas for W-CDMA). Appropriate information is maintained for the neighborcells to ensure that these cells can be scheduled at the appropriatetime to achieve the desired performance.

FIG. 12 shows a block diagram of an embodiment of multi-mode terminal150. On the downlink, an antenna 1212 receives modulated signals fromGSM and/or W-CDMA base stations (or cells) and provides a receivedsignal to a receiver unit (RCVR) 1216. Receiver unit 1216 conditions(e.g., filters, amplifies, and frequency downconverts) the receivedsignal and further digitizes the conditioned signal and provides datasamples. A demodulator (Demod) 1218 processes the data samples andprovides demodulated data. A decoder 1220 then deinterleaves and decodesthe demodulated data and provides decoded data. The processing bydemodulator 1218 and decoder 1220 is typically different for differentradio access technologies. For example, demodulator 1218 may performmatched filtering and equalization for GSM. Demodulator 1218 may performdescrambling with PN sequences, despreading with orthogonal variablespreading factor (OVSF) codes, data demodulation, and so on, for W-CDMA.For cell measurement, demodulator 1218 may process the FCCH to obtaintiming information for a GSM neighbor cell, and decoder 1220 may processthe SCH to obtain cell identification and other information for the GSMneighbor cell.

On the uplink, data (e.g., measurement reports) to be transmitted byterminal 150 is processed (e.g., encoded and interleaved) by an encoder1240 and further processed (e.g., modulated) by a modulator 1242 inaccordance with the applicable radio access technology (e.g., GSM orW-CDMA). A transmitter unit (TMTR) 1244 conditions the modulated data togenerate an uplink signal, which is then transmitted via antenna 1212 toone or more base stations (e.g., the serving cell).

A controller 1230 directs operation of various processing units withinterminal 150. A memory unit 1232 stores data and program codes used bycontroller 1230 and other processing units. Controller 1230 implementsschedulers 1236, which may include a W-CDMA scheduler, an overallscheduler, and so on. The W-CDMA scheduler determines how often and whendata samples need to be collected for W-CDMA frequencies for off-lineprocessing by demodulator 1218 and decoder 1220. The overall schedulermay schedule the neighbor cells for measurements during idle framesbased on process 800, 1100, or some other process.

For measurement scheduling, controller 1230 may receive various types ofinformation from other processing units such as, for example,measurement results for previously scheduled neighbor cells (e.g., fromdemodulator 1218 and/or decoder 1220), received signal strength for theneighbor cells (e.g., from demodulator 1218), and timing informationfrom a timer 1234. Controller 1230 maintains state information for eachGSM neighbor cell. The state information may include, for example, thestate of the cell, the elapsed time since the last scheduledmeasurement, the number of failed FCCH detection attempts, the number offailed SCH decoding attempts, the relative received signal strength ofthe cell (e.g., whether among the top M cells or not), the amount oftime since the SCH was last decoded, and so on. Different stateinformation may be maintained for different scheduling processes. Foreach idle frame, controller 1230 determines and updates the states ofthe GSM neighbor cells, ranks the GSM neighbor cells with the samestate, and selects the highest-ranking GSM cell or W-CDMA frequency foruse of the upcoming idle frame.

Timer 1234 provides timing information for controller 1230. For example,for scheme 700, timer 1234 indicates whether N seconds have elapsed foreach GSM neighbor cell in Strong SCH Unknown state 720 and SCH Unknownstate 730 and whether T seconds have elapsed for each cell in KnownConfirmed state 740. For scheme 1000, timer 1234 indicates whether Pseconds have elapsed for each GSM neighbor cell in Strong FCCH Unknownstate 1010 and Strong SCH Unknown state 1030. The operation of timer1234 is dependent on the manner in which the states are defined.

The techniques described herein for scheduling measurements of neighborcells in multiple wireless communication systems may be implemented byvarious means. For example, these techniques may be implemented inhardware, software, or a combination thereof. For a hardwareimplementation, the processing units used to perform the measurementscheduling may be implemented within one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PIDs),field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, other electronic units designed toperform the functions described herein, or a combination thereof.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory unit 1232 in FIG. 12) and executed by aprocessor (e.g., controller 1230). The memory unit may be implementedwithin the processor or external to the processor, in which case it canbe communicatively coupled to the processor via various means as isknown in the art.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. An apparatus operable to schedule measurement for cells in aplurality of wireless communication systems, comprising: a controlleroperative to categorize cells in a first wireless communication systembased on a plurality of states, prioritize the plurality of states,prioritize cells in a second wireless communication system relative tothe plurality of states, select a cell in the first system or the secondsystem based on priorities of the cells in the first and second systems,and schedule the selected cell for measurement in next available frame;and a demodulator operative to make measurement for the selected cell inthe next available frame.
 2. The apparatus of claim 1, wherein thecontroller is operative to update states of the cells in the firstsystem based at least on measurement results obtained from prior frames.3. The apparatus of claim 2, wherein the controller is operative toupdate cells in the states of the cells in the first system are furtherbased on information for number of failed attempts to acquire timinginformation, number of failed attempts to acquire cell identification,and elapsed time since last selection for measurement.
 4. The apparatusof claim 1, wherein the controller is further operative to rank cells inthe first system with same state, for each of the plurality of states,and to select a cell for measurement further based on the ranking of thecells in the first system.
 5. The apparatus of claim 1 and implementedwithin a wireless communication device.
 6. The apparatus of claim 1,wherein the first and second systems utilize different radio accesstechnologies (RATs).
 7. The apparatus of claim 1, wherein the firstsystem is a Global System for Mobile Communications (GSM) system and thesecond system is a Wideband Code Division Multiple Access (W-CDMA)system.
 8. A method of scheduling measurement for cells in a pluralityof wireless communication systems, comprising: categorizing cells in afirst wireless communication system based on a plurality of states;prioritizing the plurality of states; prioritizing cells in a secondwireless communication system relative to the plurality of states;selecting a cell in the first system or the second system based onpriorities of the cells in the first and second systems; and schedulingthe selected cell for measurement in next available frame.
 9. The methodof claim 8, wherein the first system is a Global System for MobileCommunications (GSM) system and the second system is a Wideband CodeDivision Multiple Access (W-CDMA) system.
 10. The method of claim 8,wherein the cells in the second system are periodically scheduled formeasurement.
 11. The method of claim 8, further comprising: updatingstates of the cells in the first system based at least on measurementresults obtained from prior frames.
 12. The method of claim 8, whereinthe plurality of states include an Unknown state, a Known Confirmedstate, and a Known Unconfirmed state, the Unknown state including cellsin the first system for which timing information and cell identificationare not known, the Known Confirmed state including cells in the firstsystem for which timing information is known and cell identification hasbeen confirmed within last T seconds, where T is a predetermined timeperiod, and the Known Unconfirmed state including cells in the firstsystem for which timing information is known and cell identification hasnot been confirmed within last T seconds.
 13. The method of claim 12,wherein timing information for a cell in the first system is obtained bydetecting a frequency correction channel (FCCH) and cell identificationis obtained by decoding a synchronization channel (SCH).
 14. The methodof claim 12, wherein cells with the Known Confirmed state are notscheduled for measurement.
 15. The method of claim 12, wherein cellswith the Known Unconfirmed state are given higher priority than cellswith the Unknown state.
 16. The method of claim 12, wherein theplurality of states further include a Strong SCH Unknown state and anSCH Unknown state, the Strong SCH Unknown state including cells in thefirst system for which timing information is known and cellidentification is not known and which are among M strongest receivedcells in the first system, where M is a number greater than one, and theSCH Unknown state including cells in the first system for which timinginformation is known and cell identification is not known and which arenot among the M strongest received cells in the first system.
 17. Themethod of claim 16, wherein the cells with the Strong SCH Unknown stateare given first priority, the cells with the SCH Unknown state are givensecond priority, the cells with the Known Unconfirmed state are giventhird priority, and the cells with the Unknown state are given fourthpriority among the cells in the first system.
 18. The method of claim17, wherein the cells in the second system are given higher prioritythan the cells with the Known Unconfirmed state and lower priority thanthe cells with the SCH Unknown state.
 19. The method of claim 12,wherein the plurality of states further include a Strong FCCH Unknownstate and an FCCH Unknown state, the Strong FCCH Unknown state includingcells in the first system for which timing information and cellidentification are not known and which are among M strongest receivedcells in the first system, where M is a number greater than one, and theFCCH Unknown state including cells in the first system for which timinginformation and cell identification are not known and which are notamong the M strongest received cells in the first system.
 20. The methodof claim 19, wherein cells with the Strong FCCH Unknown state and cellswith the FCCH Unknown state transition to the Unknown state after Xfailed attempt to acquire timing information, where X is one or greater.21. The method of claim 8, wherein the cells in the second system aregiven higher priority than the cells in the first system if a designatedflag is set.
 22. The method of claim 8, further comprising: rankingcells in the first system with same state, for each of the plurality ofstates, and wherein the selecting is further based on the ranking of thecells in the first system.
 23. The method of claim 22, wherein ahighest-ranking cell with highest priority is selected for measurementin the next available frame.
 24. The method of claim 23, wherein thehighest-ranking cell with the highest priority is selected formeasurement only if a frame that is used to make the measurement for thecell is potentially aligned with the next available frame.
 25. Themethod of claim 22, wherein the cells in the first system with the samestate are ranked based on received signal strength.
 26. The method ofclaim 22, wherein the cells in the first system with the same state areranked based on elapsed time since last measurement.
 27. The method ofclaim 12, further comprising: arranging cells with the Unknown stateinto a first group of A strongest received cells and a second group ofcells, where A is a number greater than one, and wherein the A cells inthe first group are selected prior to selecting a cell in the secondgroup.
 28. The method of claim 27, wherein the second group includes Bnext strongest received cells with the Unknown state, where B is anumber greater than one, wherein a third group includes remaining cellswith the Unknown state, and wherein the B cells in the second group areselected prior to selecting a cell in the third group.
 29. An apparatusoperable to schedule measurement for cells in a plurality of wirelesscommunication systems, comprising: means for categorizing cells in afirst wireless communication system based on a plurality of states;means for prioritizing the plurality of states; means for prioritizingcells in a second wireless communication system relative to theplurality of states; means for selecting a cell in the first system orthe second system based on priorities of the cells in the first andsecond systems; and means for scheduling the selected cell formeasurement in next available frame.
 30. The apparatus of claim 29,further comprising: means for updating states of the cells in the firstsystem based at least on measurement results obtained from prior frames.31. The apparatus of claim 29, further comprising: means for rankingcells in the first system with same state, for each of the plurality ofstates, and wherein a cell in the first system or the second system isselected further based on the ranking of the cells in the first system.32. A processor readable media for storing instructions operable in awireless device to: categorize cells in a first wireless communicationsystem based on a plurality of states; prioritize the plurality ofstates; prioritize cells in a second wireless communication systemrelative to the plurality of states; select a cell in the first systemor the second system based on priorities of the cells in the first andsecond systems; and schedule the selected cell for measurement in nextavailable frame.